1. Field of the Invention
The present invention relates to a method and a system for chamfering, and to a press therefor. More specifically, the invention relates to a chamfering method and a chambering system for chamfering a material, illustratively a plate or sheet blanked or punched by a press, and to a press therefor.
2. Description of the Related Art
There is disclosed a chamfering method in Japanese Patent Application Laid-Open Publication No. 6-14151 (hereinafter referred to as "first related art").
In the first related art, a core plate is laminated to form a core of a rotor of an electric motor, chamfers are formed on an upper surface of an uppermost core plate and a lower surface of a lowermost core plate, respectively, of the core. Because only the outside surfaces of the uppermost and lowermost core plates and arc subject to chamfering, and because a pressing operation is used in the sequence of laminating each of the core plates, separate chamfering operations are performed to form the chamfers on the uppermost and lowermost core plates.
Depending upon application of the member, there are of course cases in which both surfaces of the punched part will be chamfered. For example, in Japanese Utility Model Application Laid-Open Publication No. 3-124027 (hereinafter referred to as "second related art"), there is disclosure of clutch plates which are used in a coupling that transmits power via the viscous resistance of a fluid. The clutch plates each have chamfers formed at both sides thereof.
In the case of the second related art, chamfers of predetermined dimensions are formed at both surfaces of a clutch plate blank by the action of a fixed lower punch and an upper punch that has the same shape on its end part as the lower punch and is slide-dropped thereonto.
When the press chamfering operation is continued for a long period of time, however, because of such factors as thermal expansion of the press itself and the dies, minute variations in the bottom dead point (stroke end point) of the slide-dropped upper punch occur, this being accompanied directly by variations in the chamfer dimensions. In the case of the first related art, burrs may remain on the motor core plates, leading to a damage on winding wires. In the case of the second related art, the clutch plate in the coupling may get adhered to the adjacent clutch plate because of a hump. To avoid such problems, it is important to perform the troublesome task of maintaining control of accuracy of the bottom dead point of the upper punch.